Article for polishing



Patented Sept. 23, 1952 UNITED STATES Art'rio liz'ron romsniiqe 'Philip- W. PortenHigganum, Conn, assignor to D. & H. Scovil, Inc'.', Higganum, Conn, a corporation of Connecticut No Drawing. Application September 6, 1949,

Serial No. 114,275

9 Claims. (C1. 51-3298)q This invention relates to a polishing layer and to a method for preparing the layer. More par- I ticularly, the invention relates to a polishing layer which comprises finely divided abrasive par-- ticles imbedded in an adhesive matrix which ex-"- hibits characteristics of fluidity, resilienceand lubricity which makethe composition uniquely suitable for use in the manufacture of polishing implements such as'polishing wheels and polishing belts which are normally operated at high speed in frictional engagement with surfaces which it is desired to polish.

As it is well understood, commercial finishing of articles of manufacture, both ferrous and nonferrous, is ordinarily accomplished by maintainin the surface of the article in frictional engage-' ment with an endless surface, suchas that provided by a wheel or an endless belt, which is coated with an abrasive layer which 'actsto reduce the irregularities on'the surface of the article. The surface of the article is acted on successively by abrasive particles of increased fineness and the final, or polishing operation, is accomplished with an extremely fine abrasive material such as rouge. 1

It ha been observed f-requently'that an adhesive matrix, the adhesive composition in which the abrasive particles are imbedded and which adheres to the endless surface provided by a belt or wheel; which is entirelysuitable for retaining" larger abrasive particles in polishing position on the surface of the belt or wheel is not-satisfactory for polishing purposes as differentiated from cutting or surface removal purposes. Mostheavy surface removal is accomplished with grains larger than 100 mesh, and polishing is accomplished with grains smaller than 100 mesh. Silicate base binding cements are generally limited to use'with 100 mesh grains andlarger, as it is recognized that such silicate base cements are not suiiiciently resilient to permit the abrasive particles to retreat intothefilm and permit polishing action, which is accomplished partially by a a plastic flow of the metal induced bythe polishing action of the abrasive layer. Animal glues,

on the other hand, make a satisfactory matrix for fine abrasive particles, but the use of animal glues in the manufacture of a polishing device'entails several practical difficulties. For example, animal glue employed as an abrasive particle matrix must be cured within a certain range of temperature and humidity conditions, and it will polishing layer comprising finely divided abrasive particles and an'a'dhesive matrix which is char; acterized by a fluidity, resilience and lubricity which effectively retains the fine abrasive particles against displacement and which ischemicallystable during long periods of storage or exposureto the atmosphere. a f I Afurther object of the invention is to provide an i adhesive matrix for fine abrasive particles which may be' worked at normal temperatures andwhich can be cured under normal atmospheric conditions without impairing its effec tiveness.

Heretofore, with the two most common manufactured abrasive grains, silicate base cements have been used effectively only withaluminum metals, and articles of small sizes, or on tho'sedecay if it is exposed to the atmosphere for-any considerable period of time.

The object of this invention provide .a

oxide abrasive grains, and they have not'proven tobe satisfactory for bonding silicon carbide grains, apparently as a result of theevolution of gas occurring when the carbide grains are used with silicate base adhesives which prevents effective bonding of the carbide grains. It will be ap parent, therefore, that the instant adhesive matrix which does not exhibit this reaction to sili? con carbide grains willsubstantially increase the usefulness of carbide grains in the preparation of polishing implements for use on non-ferrous.

having hard surfaces. s I

It has been found that an adhesive matrix having excellent properties with respect to retaining a finely divided abrasive material, in polishing position on the endless surface of a wheel or belt which is operated at speeds which develop a high frictional heat can be formulated, by a method,

1 described more particularly hereinafter, from certain proportions of a synthetic resin and an alkali-silicate and certain diluents which, act to stabilize the matrix and enhance its workability.

The adhesive character of the matrix is ime parted by the synthetic resin and the alkali-silicate, and the diluents which are added increase the chemical stability, prevent hardening during extended periods of storage and increase the workability. These diluents comprise a poly-' hydric alcohol which apparently acts to modify the adhesive constituents as well as acting as a plasticizerand smoothing agent which prevents premature hardening of the matrix. The diluents also include a kaolintype clay of extremely fine particle size, and a carboxymethylcellulose ester which is slightly alkaline in solution which prevents premature breaking of the emulsion of the synthetic resin when, as. it is most convenient;- the synthetic resin employed is in the form of an oil-in-water type emulsion. Additionally, the carboxymethylcellulose ester also appears to improve the flexibility of the film deposited from a solution of the instant adhesive matrix.

Polyvinyl acetate is one of the synthetic resins which is suitable for usein practicing the instant invention. The polyvinyl acetatemay be employed conveniently in emulsion form. The manner in which the emulsion is prepared appears to be immaterial. It may, for example, be prepared by first polymerizing and thereafter dispersing the-polymerized vinyl acetate in water, or as described in (iota-11in. U.v S. Patent No. 2,401,445 to White, dated June 4, 1946, be prepared by carrying out the polymerization in a dispersion of the monomeric acetate. A. commercially available emulsion of polyvinyl acetate resin having a solid content of about 557% has proved to have the optimum proportion of resinous .material tor thefluidity required:tor

easeot handling Itwill. beunderstood, however, thatin the following examplesand inthe claims theemulsions referred to may be diluted or dehydrated within areasonable limit without-departing from. the scope ofathe invention.

The alkali silica found to be; most eiiective; in preparing; the. instant; composition; has an alkali to silicaratioof. about Lto 3. Asodiumsilicate of this character. is an opalescent... syrupy liquid of relatively low alkalinit and has a spccificgravity or. about 1.4. Good: results are. obtained, how ever, with other alkali-silicates.

A suitable .carboxymethylcellulose. may be. obtained by reacting sodium .monochloroacetate with alkali cellulose and substituting approximately. .751 carboxymethyl group for each anhydro glucose the resulting sodiumcarboxymethylcellulose molecule. Commercially avail-- ablegrades of this ingredient produce good results.

The character or the. clay. which. used-as a or in the instant matrixeifects importantly the character of the matrix. The essential re quirement of a satisfactory clay is extremely small particle size. A kaolin typeof clay. having a screen residue on af325imeshscreen of less, than .;2%, indicating a. particle of less than 2' microns in over 80% of the. any hassbeen. found to be satisfactory consistently. .A clay .of-this type-iscomprised principally of silica. alumina and a small amount of iron oxide.

Efiectiveness-as an adhesive matrixv for abrasive particles of less than I00. mesh is' limited to compositions'which comprise only certain proportions of the namedu'ngredients. Although the the acetate monomer factory-adhesive matrix.

workable-proportions'of each ingredient is not sharply defined, the' critical proportions appear to be, byweight, from about-4 to-36 %'0-f polyvinyl acetate water emulsion having a solid content of about 56%, '65 to 40% alkali silicate, .5. to 6% sodium carboxymethyloellulose, '26 to 16% clay, and 4.5 to 2.0% polyhydric alcohol. Any marked reduction in the proportion ofpolyhydric alcohohsorbitol being the most eiiective, will cause the adhesive composition to harden prematurely in 'shipping containers or upon extended exposure" to the atmosphere. An increase inthe amount of. polyvinyl acetate resin beycndthe maximum. specified will not materially increase the strength of the film deposited from a solution of the adhesive composition, and due to the increased. free :acetic acid present in the larger QJIIOUIItIOf polyvinyl acetate emulsion an increasedramount .of sodium carboxymethylcellw lose may be required to neutralize the composition. However, increased quantities of the sodium carboxymethylcellulose weakens the bond strength of the composition. Excesses oi sorbitol beyond the proportion specified also reduce the tensil strength and render too plastic the film depositedirom a. solution or the adhesive composition.

Although no satisfactory explanation has been developed, the order in which the ingredients are admixed is a critical factor in obtaining a satis- .Otherwise, there are no lim-iting" conditions; good results are obtained carry ng Qiltrthd process under normal conditioris otratnrospheric temperature and pressure.

Illustrating themethod of preparing the adfhesivematrix' by way of example:

Example 1 15 pounds of alkali-silicate (sodium silicate) was placed 1 in admixing "container and agitated bye revolving beater running at medium speed; fi'poundsutlraolin clay was added graduallyand continued untilthe mixture was smooth. :Lpound .ot-sorbitol-was. added and the mixinaicontmued until theisorbitol appeared to behomcgeneouslprdispersed throughout the composition. l /z pounids:oiusodium carboxymethyl-- cellulose addedandf the beating continued. Thereafter*d'poundspfippolyvinyl acetate water emulsion haying-aboutga 5,6 solid content was added. This additiongcausedthe composition to thicken. and the; beatinet-wasscontinued until the mposition-appeared; to: have; a. uniform density. Thereupon, an. aardditinnail. :6 pounds of acetate EImIISiQIL' was addedand; thebeatine-continued at medium-speedier aboutZO minutes. At the. end of this period the-composition appeared to be homogeneous and oiiuniformdensity. The composition vva thenl drawn oiii nto. shippin containers-and'allowedto stande pQsed to atmosphericr conditions. forseveral weeks. No hardening occurred; thev composition proved to be as effective-after storage as it was at the timeit was freshly drawn from the mixing container. I

'Ifhesolution,otthe-matrix was applied to the surface otanendless fabric belt and thereafter the: belt was refledinrcontaet with. finely divided abrasive-particles about 220 mesh. The belt wasallowedtdreure tel-"24 hours under normal atmospheric conditions. The belt was. then tested for polishing qualities: comparatively with belts having abrasive: particles of the same size imhedded, respectivelmin an, animalglue matrix, an. a.rtificial resinmatrixand a silicate base glue matrix. -The :belt treated a with the compositionpreparedaccording to. the foregoing exam le proved tobe. superior in maintaining the fine abrasivenartielesin polishing engagement with the article. being finishedas well as having superior'flexibility whiclllpermitted a greater area of the taco of thebelt. to be maintained in contact withlthe. article being finished. The lubrici y ofthe composition. greatly improved the heat resistance or the belt andthe belt was found, o. wear threeto. fourtimes longer than the others tested. L'Ifhe quality oftlie polishingwas improved due tame-tendency of the instant composition .to. release the. larger abrasive particles,

siliency of the adhesive. matrix also contributed to'a higher quality polishing. as minute irregularities on the surface of the article being finished appeared to be peened over into adjacent declivities rather than tornoif by the abrasive particles as would occur if the matrix in which the particles were imbedded did not yield to some extent to the irregularity on the surface of the article. I

Other preparations of the composition which proved .to be equally effective were made as follows? Example 2 The same method ofpreparation was followed as outlined in the foregoing example, using by weight a total of 9 parts polyvinyl acetate water emulsion, 15 parts alkali-silicate, 6.0 parts clay, 1.0 part sodium carboxymethylcellulose and 1.0 part sorbitol.

The adhesive composition thus prepared was made up in the manner prescribed in the foregoing example. In this instance, however, silicon carbide abrasive particles of about 100 mesh were added directly to the solution and the solution the composition prepared according to the invention is water soluble which makes it safe and easy to handle and facilitates resurfacing the is thereafter applied to the surface which is to thereafter applied to the endless surfaces of a belt and wheel. The quality of polishing obtained with the belt and wheel thus prepared was uniformly superior. I

Example 3 The same procedure outlined in Example '1 was followed using 15 pounds of sodium silicate, 6 pounds of clay, 1 pound of sorbitol, pound sodium carboxymethylcellulose, and a total of 6 pounds of polyvinyl acetate water emulsion having about 56% solid content.

The composition thus prepared was stored in shipping containers for several weeks without impairing the effectiveness of the composition.

Example 4 The procedure outlined in Example 1 was again followed, using 15 pounds of sodium silicate, 6 pounds of clay, 1 pound of sorbitol, pound of sodium carboxymethylcellulose and a total of 4 pounds of polyvinyl acetate wateremulsion having about 56% solid content.

The composition thus prepared was tested in the same way as that described in Example 1. The results were equally good.

Example 5 The procedure outlined in Example 1 was followed using 15 pounds of sodium silicate, 6 pounds of clay, 1 pound of sorbitol, /4 pound of sodium carboxymethylcellulose and a total of 2 pounds of polyvinyl acetate water emulsion having about 56% solid content. The composition thus described was tested in the same manner as that described in Example 1 with equally satisfactory results.

Example 6 The procedure outlined in Example 1 was followed using 15 pounds of sodium silicate, 6 pounds of clay, 1 pound of sorbitol, 1% pound of sodium carboxymethylcellulose and a total of 1 pound of polyvinyl acetate water emulsion having about 56% solid content. This composition was tested in the same manner as that described in Example 1 using abrasive particles of about 100 mesh.

It was noted that all the adhesive matrices within the prescribed limits of composition satisfactorily bond all sizes of abrasive grains, from the heaviest to the lightest. In this instance a high quality polishing was obtained with the belts treated with the described polishing layer.

As it is indicated in the foregoing examples,

be'treated' Furthermore, several layers of polishing material may be built up one upon the other so that'when'theuppermostlayer is worn oif the under layer will-present a polishing surface.

It will be apparent that the character of the adhesive matrix may bemodiiied to some extent to meet various particular requirements by the addition of various well known plasticizers and fillers which act to alter the smoothness. flexibility or toughness of the film deposited is well understood in the art.

If it is desired, for example, to produce a polishing implement which is suitable for working under water in a wet polishing process, the water resistance of the adhesive matrix may be increased by the addition of glyoxyl, cupric glychromate, sodium glychromate, chromic acetate, and, or alternately, heating the polishing layer to a temperature of about centigrade for several minutes to cause a fusion of the resin.

Having thus described the invention, what is new and desired to be secured by Letters Patent 1s:

1. A matrix for abrasive particles comprising by weight, 4 to 36% of polyvinyl acetate water emulsion having a solid content of about 56%, 65 to 40% alkali-silicate, .5 to 6% sodium carboxymethylcellulose, 26 to 16% clay, and 4.5 to 2.0% sorbitol.

2. A matrix for abrasive particles comprising by weight 9 parts polyvinyl acetate water emulsion having about 56% solid content, 15.0 parts alkali-silicate, 6.0 parts clay, 1.0 part sodium carboxymethylcellulose and 1.0 part sorbitol.

3. A matrix for abrasive particles comprising by weight 4.0 parts polyvinyl acetate water emulsion having about 56% solid content, 15.0 parts alkali-silicate, 6.0 parts clay, .5 part sodium carboxymethylcellulose, and 1.0 part sorbitol.

4. A matrix for abrasive particles comprising by weight 1.0 part polyvinyl acetate water emulsion having about 56% solid content, 15.0 parts alkali-silicate, 6.0 parts clay, .1 part sodium carboxymethylcellulose and 1.0 part sorbitol.

5. A composition for depositing a polishing layer comprising abrasive particles dispersed in an adhesive composition comprising by weight 4 to 36% of polyvinyl acetate water emulsion having a solid content of about 56%, 65 to 40% alkalisilicate, .5 to 6% sodium carboxymethylcellulose, 26 to 16% clay, and 4.5 to 2.0% sorbitol.

6. A composition for depositing a polishing layer comprising abrasive particles dispersed in an adhesive matrix comprising by Weight 12 parts polyvinyl acetate water emulsion having about 56% solid content, 15 parts alkali-silicate, 6.0 parts clay, 1.5 parts sodium carboxymethylcellulose and 1.0 part sorbitol.

7. A composition for depositing a polishing la er comprising abrasive particles dispersed in an adhesive matrix comprising by weight 6.0 parts polyvinyl acetate water emulsion having about 56% solid content, 15.0 parts alkali-silicate, 6.0

parts. clay, l-75'part sodium,eerboxymethylcellulose and. 1.9 pertsorbitol. v

8.;A compo ition for vdepositing apolishing layer, comprising abrasive particles dispersed in an adhesive matrix .oomprising by weightzn 5 parts polyvinyl. acetate water emulsion; having about 56 solid content, l5-.0,.pe1ts alkali-silicat 6.0 parts. clay, .25 part sodium eerboxymethylcellulose,. and 1.01 partsorbitol 9. A polishing implement comprisihgfe, liody 10 2,4

having eflexible surface, a poli'shing la yr adhering to said suriecesaidlaxer includin br sive particles dispersed inenr adhesivemaitrix comprising byweight abouflzfl 110 20% of. p Iyvinylacetatefifi to 40% alkali-silicate, .5 ice-6% sodium cerboxymethylcellulose 26 to 16% elay, and 4.5 to 2.0% surbitol.

r W. PQRTER.

. es LBZEFERENOES CITED fiihe; following: references are of record ,in' the file of this patent:

UNITED STATES PATENTS Number Name Date 2,111,272 Paulson Mar. 15, 1938 2,124,055 Courtney July 19. 1938 2,465,295 Strauss Mar. 22, 1949 Murphy'et a1. Nov. 1 1949 I FOREIGN -PATEN'I'S Number v Country r Date- ;462,697 GreatfBribain Mar. 15, 1937' 

9. A POLISHING IMPLEMENT COMPRISING A BODY HAVING A FLEXIBLE SURFACE, A POLISHING LAYER ADHERING TO SAID SURFACE, SAID LAYER INCLUDING ABRASIVE PARTICLES DISPERSED IN AN ADHESIVE MATRIX COMPRISING BY WEIGHT ABOUT 2.24 TO 20% OF POLYVINYL ACETATE, 65 TO 40% ALKALI-SILICATE, .5 TO 6% SODIUM CARBOXYMETHYLCELLULOSE, 26 TO 16% CLAY, AND 4.5 TO 2.0% SORBITOL. 